Display contrast

ABSTRACT

Display devices with improved display contrast and methods of manufacturing the display devices. Some embodiments include a method of manufacturing a light emitting diode (LED) array. The method includes forming two mesa areas on a substrate, where a trench is defined between the two mesa areas. A pixel and a N-bus formation is formed on each of the two mesa areas to create a first LED and a second LED separated by the trench between the two mesa areas. At least a portion of the trench is filled with a non-transparent or substantially non-transparent polymeric material that absorbs light emitted from the first and second LEDs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/261,922, filed Jun. 20, 2014, which is a National Phase applicationof International Application No. PCT/GB2012/053192, filed Dec. 19, 2012,which claims the benefit of United Kingdom Application No. 1121864.1,filed Dec. 20, 2011, each incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to electronic components with improveddisplay contrast and a method of manufacturing such electroniccomponents. More particularly, the present invention relates toelectronic components having improved display contrast by using anon-transparent or substantially non-transparent material to block lightfrom an emitter source to surrounding components such as emitters,sensors or components of this nature.

BACKGROUND OF THE INVENTION

Polyimide is commonly used for planarizing semiconductor devices and toprovide electrical isolation between interconnected structures. A goodexample has been demonstrated by Horng et al. in US patent application2011/0092005, which is incorporated herein by reference. A paralleladdressed array of macro LEDs with improved reliability was achieved byusing polyimide to fill the gap between the macro LEDs. Another commonapplication is polyimide encapsulation of LEDs to improve the lightextraction efficiency because of the increased refractive index such asdescribed by Chen et al. in US patent application 2011/0024720, which isincorporated herein by reference. In contrast to the proposed presentinvention the polyimide used in these applications is transparent orwhat is known as having a high optical clarity.

This document is applicable to all LED arrays. For the descriptionprovided it is mainly concerned with the difficulties in manufacturingmicro-LED structures which in this case will refer to any LED structureof less than 100 microns diameter. There are a number of known andexisting problems with micro-LED arrays. For example, there is strongoptical crosstalk between adjacent pixels in conventional LED arrays,resulting in the LED display having poor contrast. To form amatrix-addressable LED array, isolated LED mesa columns need to beformed by dry etch. The large height difference, the sloped mesa and thesharp edges formed in the trench cause undesirable light scattering(bars surrounding the pixels), and thus reduce the display contrast ofthe LED array.

A further known problem with LED arrays is a reliability issueassociated with the isolation layer. Conventionally, the isolation layerof p-contacts from n-contacts of a matrix LED array is made fromdielectric materials (e.g. silicon oxide or silicon nitride). Forinstance, Dawson et al. in US patent US2006/0110839 A1, which isincorporated herein by reference, uses SiO₂ to isolate the mesa withsloped sidewall. Although the sloped mesa can alleviate the stepcoverage issue of the dielectric layer normally associated with standardtechniques, the device made this way can still have reliability issues,resulting in undesirable electric crosstalk or shorting. This is mainlydue to the fact that the thin dielectric layer cannot reliably cover themesa with a large height, and it may be stripped off during subsequentprocess due to possible adhesion issues. All of these factors mean thatthe devices need to be carefully manufactured to ensure that thesidewall is suitably angled and that there are no contaminants (e.g.pin-holes) which could cause electrical crosstalk.

The present invention seeks to overcome these said disadvantages andproblems.

It is an object of at least one aspect of the present invention toobviate or mitigate at least one or more of the aforementioned problems.

It is a further object of at least one aspect of the present inventionto provide improved micro-LED arrays with improved display contrast andreduced optical cross-talk.

It is a further object of at least one aspect of the present inventionto provide an improved method for manufacturing micro-LED arrays withimproved display contrast and reduced optical cross-talk.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is providedan array of integrated LED devices. This may involve a micro-LED arraycomprising:

at least two raised mesa areas;

located between the at least two raised mesa areas there is a trench;

on the upper surface of the at least two raised mesa areas there arepixels and N-bus formations along with an annealed metal area and ap-metal layer;

wherein the trench is at least partially filled with a non-transparentor substantially non-transparent material capable of blocking lightemitted from within the micro-LED array.

The present invention therefore resides in the provision of using anon-transparent or substantially non-transparent material to block lightfrom an emitter source to surrounding components such as emitters,sensors or components of this nature. This non-transparent orsubstantially non-transparent material is used to reduce unwantedcrosstalk and thereby provide improved display contrast for micro-LEDarrays and the like.

The non-transparent or substantially non-transparent material maytherefore fill the trench in adjacent pixels. Although the actualthickness of the deposited non-transparent or substantiallynon-transparent material is not important sufficient material should beintroduced so that redirected light should be absorbed and preventedfrom being emitted from the upper surface.

The non-transparent or substantially non-transparent material may fullyoccupy the trench or may simply form a layer.

The non-transparent or substantially non-transparent material may beseen as functioning as an interlayer dielectric.

The non-transparent or substantially non-transparent material may beselected from any appropriate material that is capable of blockinglight. For example, the material may be selected from any suitablepolymeric material such as anyone of or combination of the following:polyimide; epoxy; and benzocyclobutene.

In particular embodiments there is a combination of different polymersforming a light blocking layer. For example, there may be a combinationof polymer and other dielectric layers such as but not limited tosilicon nitride and/or silicon dioxide.

The non-transparent or substantially non-transparent material forms alayer which is non-transparent or substantially non-transparent to lightat the emission wavelength of the micro-LED array. The non-transparentor substantially non-transparent material may therefore be matched toblock the light emitted from the micro-LED array. The material may bedesigned to have a non-transparent surface layer or gradednon-transparent layer.

A further advantage of the non-transparent or substantiallynon-transparent material in polymeric form is that the polymeric layerallows metals such as deposited p-metal layer to be conformablydeposited thereby further reducing the light scattering from the trench(i.e. cavity). The polymeric material may also provide optical andelectrical isolation between emitters of varying wavelength emissionsand/or of different structural design and/or other integratedcomponents.

It has been found that the deposited non-transparent or substantiallynon-transparent material may also function to effectively isolate eachpixel and p-contact from n-contacts, thereby eliminating the undesirableelectric crosstalk and improving the device reliability.

According to a second aspect of the present invention there is provideda method of manufacturing a micro-LED array comprising:

forming at least two raised mesa areas wherein located between the atleast two raised mesa areas there is a trench;

on the upper surface of the at least two raised mesa areas formingpixels and N-bus formations along with an annealed metal area and ap-metal layer; and

wherein the trench is at least partially filled with a non-transparentor substantially non-transparent material capable of blocking lightemitted from within the micro-LED array.

The manufactured micro-LED array may be as defined in the first aspect.

The mesa areas may be formed using a dry etch technique.

The non-transparent or substantially non-transparent material may bedeposited into the trench using any suitable deposition technique toform a layer or fully fill the trench up to the same level as the heightof the mesa areas.

The non-transparent or substantially non-transparent material may becured.

The pixels and N-bus formations may be formed on the upper surface ofthe mesa areas using any suitable technique.

A metal layer (e.g. a p layer) may be formed onto etched areas on theupper surface of the mesa areas.

According to a third aspect of the present invention there is provided aflip-chip device comprising non-transparent or substantiallynon-transparent material capable of blocking light.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIGS. 1 and 2 are micro-LED arrays according to the prior art showingsignificant crosstalk;

FIG. 3 is a micro-display image from a conventional matrix device usingSiO₂ as the isolation layer between mesa and from the image whereelectric crosstalk and open circuit (due to metal coverage issue on theSiO₂) are evident;

FIG. 4 is a micro-display image from a micro-LED array device accordingto the present invention where there is no electric crosstalk and opencircuit are observed;

FIG. 5 is a cross-sectional side view of a micro-LED array according tothe present invention;

FIG. 6 is a top view of a micro-LED array according to the presentinvention; and

FIGS. 7 to 14 show a method of forming micro-LED arrays according to thepresent invention.

BRIEF DESCRIPTION

Generally speaking, the present invention resides in the provision ofusing a non-transparent or substantially non-transparent material toblock light from an emitter source to surrounding components such asemitters, sensors or components of this nature. This non-transparentmaterial is used to reduce unwanted crosstalk and thereby provideimproved display contrast for micro-LED arrays and the like.

FIGS. 1 and 2 are views of arrays according to the prior art generallydesignated 100, 200 where there are a plurality of LEDs 112, 212 showingsignificant crosstalk between them. The LEDs 112, 212 when activatedhave a ‘halo’ effect and show poor display contrast. In the array 100there is a block of LEDs 112 where there is poor contrast with as muchas 20% of the light measured from the surrounding area outside the areaof the LED 112.

FIG. 3 is a micro-display image 300 from a conventional matrix deviceaccording to the prior art using SiO₂ as the isolation layer betweenmesa and from the image. Electric crosstalk and an open circuit (due tometal coverage issue on the SiO₂) are evident due to the very poor imagecontrast.

FIG. 4 is a micro-display image from a micro-LED array device 400according to the present invention where there is no electric crosstalkand open circuit are observed. There is therefore a much improved imagecontrast.

FIG. 5 is a cross-sectional side view of a micro-LED array 500 accordingto the present invention. As shown in FIG. 5 there are three mesaregions generally designated 512, 524, 516. The mesa regions 512, 524,516 protrude upwards and have flat top sections in the form of, forexample, truncated cones. The important aspect to note from FIG. 5 isthat between mesa regions 512 and 514 there is an open space 518 (i.e. atrench) and no in-filling. Between mesa regions 514 and 516 the space isfilled with a non-transparent or substantially non-transparent material520 to block light. For example, the non-transparent or substantiallynon-transparent material 520 is a polyimide. In the trench between mesaregions 512 and 514, FIG. 5 shows that light rays 522 exit the lowersurface and enter the open space 518 area and are therefore capable ofreducing display contrast. In the trench between mesa regions 514 and516 the non-transparent or substantially non-transparent material 520blocks the lights rays 524 and prevents the light rays contaminating thearea around the LED light emitting areas thereby maintaining a highdisplay contrast.

In the present invention the non-transparent or substantiallynon-transparent material 520 is therefore introduced (e.g. deposited) tofill the trench between adjacent pixels. Although the actual thicknessof the deposited non-transparent or substantially non-transparentmaterial 520 is not important sufficient material should be introducedso that redirected light should be absorbed and prevented from beingemitted from the upper surface. The thickness of the non-transparent orsubstantially non-transparent material 520 may be more or less than thethickness of the mesa structure. Consequently, the light from the LEDsidewall can enter the polyimide at a larger range of incident angleowing to the increase in refractive index where the light is thenabsorbed or partially absorbed by the polymer layer. This helps tofurther improve display contrast.

The deposited non-transparent or substantially non-transparent material520 can also function to compensate the height difference of differentmesa regions, such that the metal layer on the polyimide can bedeposited in a conformal layer, further reducing the light scatteringfrom the trench.

The deposited non-transparent or substantially non-transparent material520 can also function to effectively isolate each pixel and p-contactfrom n-contacts, thereby eliminating the undesirable electric crosstalkand improving the device reliability.

Owing to the large refractive index difference between the semiconductorand surrounding mediums a significant portion of the light is typicallytrapped in the semiconductor layer which leads to phonon recombinationeffects causing unwanted and potentially damaging thermal build-up. Theintroduction of a polymer results in more of the light “escaping” plusincreases the volume of material and the thermal conductivity to improveheat dissipation. An opaque polymer surface layer can also be formed byannealing the polymer in an oxygen atmosphere.

FIG. 6 is a top view of a micro-LED array 600 according to the presentinvention where non-transparent or substantially non-transparentmaterial is deposited to fill the trench in adjacent pixels. Theemitting LED therefore has a very good display contrast and has a muchreduced ‘halo’ effect and crosstalk. The contrast between the LEDemitter and the surrounding area is therefore high.

FIGS. 7 to 14 show a method of forming micro-LED arrays according to thepresent invention. FIG. 7 shows two mesa regions 612, 614 formed by dryetch. In FIG. 8, two pixels 616, 618 are formed on the upper surface ofthe mesa regions 612, 614. FIG. 9 shows N-bus formation 620, 622 on theupper surface on the mesa regions 612, 614. In FIG. 10 a non-transparentor substantially non-transparent material (e.g. polyimide) 624 isdeposited to fill the trench between pixels and as shown extends overthe upper surface of the mesa regions 612, 614 and the pixels 616, 618and the N-bus formations 620, 622. FIG. 11 then shows there is curing ofthe non-transparent or substantially non-transparent material (e.g.polyimide) 624 with areas 626, 628 etched above the pixels 616, 618. Asshown in FIG. 12 metal 630, 632 is spread into and annealed into theetched areas 626, 628. A p-metal 634 is then deposited as shown in FIG.13. FIG. 14 shows the final array which can be topside and backsideemitting.

Whilst specific embodiments of the present invention have been describedabove, it will be appreciated that departures from the describedembodiments may still fall within the scope of the present invention.For example, any suitable type of non-transparent or substantiallynon-transparent material may be used to block light and improve thedisplay contrast on not only array devices but also flip-chip devices.

The invention claimed is:
 1. A method of manufacturing a light emittingdiode (LED) array comprising: forming a first mesa area and a secondmesa area, wherein a trench is defined between the first and second mesaareas; forming a pixel and a N-bus formation on each of the first andsecond mesa areas to create a first LED at the first mesa area and asecond LED at the second mesa area; and filling at least a portion ofthe trench with a non-transparent or substantially non-transparentpolymeric material that absorbs light emitted from the first and secondLEDs.
 2. The method of claim 1, wherein the polymeric material is oneof: polymide, epoxy, or benozcyclobutene.
 3. The method of claim 1,wherein: forming the pixel and the N-bus formation on the first mesaarea includes defining a first space between the pixel and the N-busformation; and filling the at least a portion of the trench with thepolymeric material includes filing the first space between the pixel andthe N-bus formation to electrically isolate the pixel and the N-busformation.
 4. The method of claim 3, further comprising: etching asecond space within the polymeric material above the pixel of the firstmesa area; and depositing a metal within the space.
 5. The method ofclaim 4, further comprising depositing a metal layer on top of thepolymeric material and the metal within the second space to electricallyconnect pixels of the first and second mesa areas.
 6. The method ofclaim 5, wherein; the first and second mesa areas are of differentheights; and the polymeric material provides a conformal layer fordepositing the metal layer.
 7. The method of claim 1, wherein formingthe first mesa area and the second mesa area includes performing dryetching on a semiconductor layer.
 8. The method of claim 1, furthercomprising curing the polymeric material subsequent to filling the atleast a portion of the trench with the polymeric material.
 9. The methodof claim 1, wherein the first and second mesa areas are formed on asemiconductor layer, and the polymeric material at the trench absorbsthe light emitted from the first and second LEDs and propagated throughthe semiconductor layer.
 10. The method of claim 1, wherein filling theat least a portion of the trench with the polymeric material includesannealing the polymeric material in an oxygen atmosphere.
 11. The methodof claim 1, wherein the first and second LEDs are micro-LEDs.
 12. Themethod of claim 1, wherein filling the at least a portion of the trenchwith the polymeric material includes forming a polymeric material layerover the first and second mesa areas.
 13. A light emitting diode (LED)array, comprising: a first mesa area; a second mesa area, a trenchdefined between the first and second mesa areas; a pixel and N-busformation on each of the first and second mesa areas to form a first LEDat the first mesa area and a second LED at the second mesa area; and anon-transparent or substantially non-transparent polymeric materialwithin the trench to absorb light emitted from the first and secondLEDs.
 14. The LED array of claim 13, wherein the polymeric material isone of: polymide, epoxy, or benozcyclobutene.
 15. The LED array of claim13, wherein the non-transparent or substantially non-transparentpolymeric material fills a space between the pixel and the N-busformation on the first mesa area to electrically isolate the pixel andthe N-bus formation.
 16. The LED array of claim 15, wherein: thepolymeric material defines a second space within the polymeric materialabove the pixel of the first mesa area; and the LED array furtherincludes a metal deposited within the second space.
 17. The LED array ofclaim 16, further comprising a metal layer on top of the polymericmaterial and the metal within the second space to electrically connectthe pixels of the first and second mesa areas.
 18. The LED array ofclaim 17, wherein: the first and second mesa areas are of differentheights; and the polymeric material provides a conformal layer for themetal layer disposed on top of the polymeric material.
 19. The LED arrayof claim 13, wherein the first and second mesa areas are formed on asemiconductor layer, and the polymeric material at the trench absorbsthe light emitted from the first and second LEDs and propagated throughthe semiconductor layer.
 20. The LED array of claim 13, wherein thefirst and second LEDs are micro-LEDs.